Before containers, such as beverage bottles, are labeled, they are normally moved to an appropriate target rotary position with respect to the labeling device in question. To this end, it is known e.g. from DE 10 2005 050 902 A1 and DE 10 2009 020 919 A1 to conduct the containers, while they are rotating about their main axis, past a camera system so as to image the whole circumference of the containers in a plurality of camera pictures for identifying a feature on the container surface, e.g. a molding seam. The actual rotary position of the container is ascertained on the basis of the identified feature and the container is moved to a target rotary position as a starting point for labeling.
This, however, entails the following problems:
1. In the case of comparatively small features, such as a molding seam on the surface of the container, the contours of the feature will only cause comparatively weak differences in contrast in the reflected incident light. This may perhaps not suffice for allowing an exact determination of the position of the feature, in particular when an only weakly contoured feature is seen in a view that is substantially a front view. Hence, the actual rotary position of the container cannot be determined, or only be determined with insufficient accuracy on the basis of said feature.
2. Contours of elevated features are shown with different contrast differences and/or edge widths at different rotary positions, i.e. at different object angles. Also this may have the effect that the position and/or the rotary position of a relief-like feature on the container surface can be determined only with insufficient accuracy or reliability.
3. In the areas of the features to be identified, the diameter of the container may exhibit certain tolerances, which result from the manufacturing process and which are relevant to position determination. Depending on the dimensional accuracy of the container to be examined, this may lead to an object angle-dependent inaccuracy in the determination of the position or rotary position of the identified feature. Therefore, it may be impossible to calculate a correct correction angle for moving the container to a target rotary position for subsequent labeling.
As suggested in DE 10 2005 050 902 A1, the last mentioned problem can be solved by aligning the containers in successive inspection units with increasing accuracy. In addition to the considerable complexity of equipment and the large amount of time required, the problems specified under 1 and 2 can, however, not be solved or may even be aggravated by this course of action.
Hence, there is a need for devices and methods for aligning containers, in particular for a subsequent labeling of containers, which have been improved in this respect.